The disclosure herein relates to monitoring delivery of fluids from, for example, a fluid delivery system (e.g., an infusion pump, such as a syringe pump). More particularly, the disclosure relates to detection of an abnormality in the delivery of such fluids (e.g., fluid flow occlusion due, for example, to an obstructed line in the fluid delivery system).
Infusion devices are used for the delivery of medical fluids in various situations, e.g., such as the delivery of medical fluids for an extracorporeal blood circuit, drug infusion, etc. For example, infusion devices may be usefully applied for infusing an anticoagulant in an extracorporeal circuit operatively associated with a machine for extracorporeal blood treatment. Such extracorporeal treatments may include removal of blood from the patient, external treatment thereof away from the human body, followed by its return to the patient. For example, extracorporeal blood may be made to circulate through a circuit comprising, in general, an arterial line, or blood removal line, which takes the blood from the patient to a blood treatment device (e.g., a dialyzer filter) and a venous line, or blood return line, which returns the treated blood to the patient.
To reduce the risk of coagulation of the extracorporeal blood, infusion of an anticoagulant (e.g., heparin) into the extracorporeal circuit may be used (e.g., generally into the arterial line, through an infusion line, with relatively low infusion flow rates). An infusion device that may be used, for example, to deliver the anticoagulant may include a syringe pump. For example, the syringe pump may include a pushing element, operable on command of a linear actuator, to push a plunger of the syringe containing the anticoagulant at an advancement rate which is predetermined (e.g., relatively slow). For example, in a dialysis treatment, the syringe may contain a quantity of anticoagulant necessary for several hours of treatment. The pushing element and the actuator may be part of the extracorporeal treatment machine (e.g., a dialysis machine), while the syringe may be of the single-use type (e.g., of the disposable type).
Such extracorporeal treatment machines or systems, as well as other apparatus that employ infusion devices, may also include monitoring techniques relating to the occurrence of overpressures developing internally in the syringe (e.g., pressures due, for example, to occlusions in the infusion line, with a consequent interruption in the infusion flow). The delay between the occurrence of an occlusion and its detection, as well as, for example, the provision of an alarm associated with such detection (e.g., an acoustic alarm or other form of alarm), is relevant in terms of patient safety. For example, clinical practices teach that a loss of anticoagulant infusion for more than fifteen minutes may cause the formation of blood clots in the extracorporeal circuit which, if not quickly identified, may become nuclei of bigger and progressively-growing clots.
Various security techniques relating to the detection of occlusions have been described. For example, U.S. Pat. No. 5,295,967 to Rondelet et al., entitled “Syringe Pump Having Continuous Pressure Monitoring and Display”, describes a syringe pump that includes a force transducer for continuously monitoring the force on the syringe plunger, a microprocessor for converting the measured force into a syringe pressure reading, and a display on which the syringe pressure continuously appears in order for the syringe pressure to be monitored during pumping.
Further, for example, U.S. Pat. No. 5,087,245 to Doan, entitled “System and Method for Detecting Abnormalities in Intravascular Infusion”, describes systems and methods to detect occlusions by producing perturbations of fluid flow by varying the flow rate of the fluid with respect to an equilibrium flow rate, measuring a pressure level of the fluid over a period of time to determine equilibrium pressure and a pressure response of the fluid to the perturbation, determining a first integral of the difference between the equilibrium pressure and the pressure response, determining resistance to fluid flow based on the integral, determining a second integral of the product of time and the difference between the pressure response and equilibrium pressure, and determining a compliance value by dividing the second integral by the first integral. Such resistance and compliance values are displayed, and an alarm is generated when the resistance or compliance parameters fall outside of reference ranges.
However, many known detection techniques exhibit various drawbacks. For example, they are not able, in good time, to signal a risk of occlusion in an infusion line when the infusion flow rate is very low (e.g., such as flow rates of an infusion device delivering anticoagulant in an extracorporeal circuit). Further, for example, the high variability in syringe characteristics and operating conditions are not easily taken into consideration without complex detection algorithms.